Spin squeezing and quantum correlations

We discuss the notion of spin squeezing considering two mutually exclusive classes of spin-s states, namely, oriented and non-oriented states. Our analysis shows that the oriented states are not squeezed while non-oriented states exhibit squeezing. We also present a new scheme for construction of spin-s states using 2s spinors oriented along different axes. Taking the case of s=1, we show that the ‘non-oriented’ nature and hence squeezing arise from the intrinsic quantum correlations that exist among the spinors in the coupled state.     

Theory of sheath in a collisional multi-component plasma

The aim of this brief report is to study the behaviour of sheath structure in a multi-component plasma with dust-neutral collisions. The plasma consists of electrons, ions, micron size negatively charged dust particles and neutrals. The sheath-edge potential and sheath width are calculated for collisionally dominated sheath. Comparison of collisionless and collisionally dominated sheath are made.     

Analysis of a shielded TE011 mode composite dielectric resonator for stable frequency reference

Analysis of a TE₀₁₁ mode composite sapphire-rutile dielectric resonator has been carried out to study the temperature variation of resonance frequency, close to the Cs atomic clock hyperfine frequency of 9.192 GHz. The complementary behavior of dielectric permittivity with temperature of the composite has been exploited to obtain the desired turning point in the resonant frequency. The frequency of the composite structure is found to be independent of the shield diameter beyond four times the puck diameter.     

Positron annihilation spectroscopy studies of implanted polymer membranes

Two different polymer membranes, polyethylene and Nafion, have been sequentially implanted under vacuum at room temperature with 90 keV copper ions up to 10¹⁷ ions/cm²; after each implantation step, the targets were subjected to analysis with Positron annihilation lifetime spectroscopy and coincidence Doppler broadening spectroscopy. Both membranes revealed a similar behavior regarding the high fluence superficial implantation, but with different degree of magnitude. In order to endorse the Positrons annihilation spectroscopy results, scanning electron microscopy coupled with energy‐dispersive energy has been performed on the same targets, despite its lower sensitivity.     

Clean photochemical synthesis mediated by radical-radical reactions: radical buffer or the persistent free radical effect?

[reaction: see text] A new synthetic methodology is reported that takes advantage of the persistent free radical effect (PFRE), where clean products can be obtained in good yields from radical cross-combination reactions, despite their reputation for being of little synthetic value and for resulting in complex mixtures; these problems can be avoided when the PFRE is used as a synthetic tool.     

Greatly attenuated reactivity of nitrile-derived carbon-centered radicals toward oxygen

Several cyanoalkyl radicals are reported to be unreactive toward oxygen; spin delocalization on nitrogen is proposed to be the most important factor to explain this unusual behaviour.     

The Persistent Radical Effect: From Mechanistic Curiosity to Synthetic Tool

The Fischer–Ingold persistent radical effect (PRE) provides a simple conceptual framework to rationalize reactivities in systems involving two radicals with very different self‐reaction rate constants; in a limiting, but rather common case, one of these radicals is persistent at room temperature. In these cases, the cross‐coupling product is strongly favored. This contribution summarizes some of the work carried out at the University of Ottawa, where the PRE plays a key role in determining product distributions. Much of this work was inspired by the seminal contributions of Hanns Fischer.     

Synthesis,characterization, and evaluation of [Ir(ppy)2(vpy)Cl] as a polymer-bound oxygen sensor

This study reports new luminescent oxygen sensors in which the luminophore is covalently bound to the polymer matrix and compares their behavior to related sensors in which the luminophore is dispersed within the matrix. The cyclometalated iridium complex [Ir(ppy)(2)(vpy)Cl], 1, has been synthesized and characterized spectroscopically (absorption and emission) and by 1-D and 2-D (1)H NMR, elemental analysis, and X-ray crystallography. Complex 1 was attached via hydrosilation to hydride-terminated poly(dimethylsiloxane) (PDMS), yielding material 2. Successful luminophore attachment was determined spectroscopically from the emission properties, and through the altered physical behavior of 2 compared to a dispersion of 1 in PDMS. Hydrosilation of 1 with dimethylphenylsilane yielded [Ir(ppy)(2)(DMPSEpy)Cl], 3, which was fully characterized and used to probe the effect of hydrosilation on the spectroscopic properties of the luminophore. Evaluation of 2 as a luminescent oxygen sensor revealed significantly improved sensitivity over dispersions of 1 in PDMS. Material 2 was also blended with polystyrene (PS) to improve the physical properties of the sensor films. The blend sensors exhibited increased sensitivity relative to films of 2 alone and maintained short response times to rapid changes in air pressure. In contrast, 1 partitioned into the PS phase when dispersed in a PDMS/PS blend, resulting in longer sensor response times.     

Pressure dependence of the superconducting state parameters of metallic glass superconductor Mg70Zn30

Explicit expressions have been derived for the volume dependence of electron-phonon coupling strength (λ) and the Coulomb pseudopotential (μ^*) considering the variation of Fermi momentum (κ _F) and Debye temperature (θ _D) with volume. Ashcroft’s model pseudopotential and RPA form of dielectric screening have been used for obtaining pressure dependence of transition temperature (T _C) and the logarithmic volume derivative (Φ) of the effective interaction strength (N ₀ V) for metallic glass superconductor Mg₇₀Zn₃₀. It has been observed that T _C of the metallic glass Mg₇₀Zn₃₀ decreases rapidly with increase of pressure and the superconducting phase disappears at about 30% decrease of volume, for which the μ^* curve shows a minimum and an elbow is formed in the Φ graph.     

Photophysical properties of fluorescent DNA-dyes bound to single- and double-stranded DNA in aqueous buffered solution.

The absorption and fluorescence spectra, fluorescence quantum yields, lifetimes and time-resolved fluorescence spectra are reported for nine different fluorescent DNA-dyes. The work was initiated in search of a quantitative method to detect the ratio of single-to-double stranded DNA (ssDNA/dsDNA) in solution based on the photophysics of dye-DNA complexes; the result is a comprehensive study providing a vast amount of information for users of DNA strains. The dyes examined were the bisbenzimide or indole-derived stains (Hoechst 33342, Hoechst 33258 and 4',6-diamidino-2-phenylindole), phenanthridinium stains (ethidium bromide and propidium iodide) and cyanine dyes (PicoGreen, YOYO-1 iodide, SYBR Green I and SYBR Gold). All were evaluated under the same experimental conditions in terms of ionic strength, pH and dye-DNA ratio. Among the photophysical properties evaluated only fluorescence lifetimes for the cyanine stilbene dyes allowed a convenient differentiation between ssDNA and dsDNA. The bisbenzimide dyes showed multiexponential decays when bound to either form of DNA, making lifetime-based analysis cumbersome with inherent errors. These dyes also presented biexponential decay when free in aqueous buffered solutions at different pH. A mechanism for their deactivation is proposed based on two different conformers decaying with different kinetics. The phenanthridinium dyes showed monoexponential decays with ssDNA and dsDNA, but there was no discrimination between them. High dye-DNA ratios (e.g. 1:1) resulted in multiexponential decays for cyanine dyes, resulting from energy transfer or self-quenching deactivation. Shifts in both absorption and fluorescence maxima for both ssDNA and dsDNA DNA-cyanine dye complexes were small. Broadening of dye-ssDNA absorption and fluorescence bands for the cyanine dyes relative to dye-dsDNA bands was detected and attributed to higher degrees of rotational freedom in the former.